A look at atrial septal aneurysm

Case report

A 53-year-old female presents with transient left side weakness which slowly improves over three days thereafter. Patient has a few years’ history of on-and-off palpitations. Clinical examination reveals an irregular pulse at 102 beats per minute (bpm), pulse deficit of 6 bpm, and 130/80mmHg blood pressure. Peripheral pulses are normal. Cardiovascular system examination confirms irregular heart. Although heart sounds are normal, a systolic click and a grade iii/iv systolic murmur in the pulmonary area is heard. Central nervous system examination reveals mild weakness in left lower limb. Patient is nevertheless able to walk unsupported. Hemogram, serum lipids, kidney function tests and liver function test results are within normal range. The echocardiogram reveals atrial fibrillation with a ventricular rate of 90/min, normal QRS and T waves. Chest X-ray shows normal cardiac size and clear lungs. Computerised tomography of the brain is normal and shows no evidence of hemorrhage. Transthoracic echocardiography reveals normal-size chambers, valves, and a prominent moderator band in right ventricle. Intraventricular septum is intact. Intra-atrial septum shows a large bulge in fossa ovalis area towards right atrium with limited excursions of this part of the atrial septum. No evidence of thrombus in any chamber or atrial appendage nor evidence of shunt (Figures 1, 2, 3). Carotid Doppler and ultrasound studies are normal. 


Fig. 1 Transthoracic echocardiography of heart

a) Apical 4-C view 

 

b) Apical 4-C view, annotated. 

 

c) Subcostal view, annotated. 


Patient has ischemic cerebrovascular embolic stroke with left side hemiparesis, atrial fibrillation with atrial septal aneurysm fossa ovalis. The ischemic cerebrovascular incident is most likely a cardioembolic stroke.
Atrial septal aneurysm is rare (ASA) and is most often an accidental finding. However it could be a contributing factor to cardioembolic stroke even though no thrombus in aneurysm or left atrium can be seen in transthoracic echo. Patient was started on anticoagulants and rate control for atrial fibrillation.

Background

Although exact definitions of ASA vary according to size (2, 3, 7), and stage (mobility) of the aneurysm (17, 18), atrial septal aneurysm is a localised 'saccular' deformity, generally at the level of the fossa ovalis, which protrudes to the right or left atrium, or on both sides. Albeit rare, atrial septal aneurysm is a well recognised cardiac abnormality. Previously diagnosed during autopsy only, it is now frequently picked up on routine echocardiography or during evaluation of ischemic stroke. Studies link it with peripheral embolism and cardioembolic stroke, pulmonary embolism and atrial arrhythmias, even though clinical significance is uncertain. Further, it can be secondary to interatrial pressure difference or may be the result of a primary malformation involving the fossa ovalis region or the entire septum (1). In patients with chronically elevated atrial pressures, as in mitral stenosis, atrial septal aneurysms are also rare: therefore acquired origin seems unlikely. Congenital malformation of the atrial septum probably contributes to development of ASA, as was suggested by Hanley PC and colleagues (2).

Associated cardiac abnormalities

Atrial septal aneurysm may be isolated or associated with another anomaly. Commonest association is patent foramen ovale (PFO). Silver and Dorsy found patent foramen ovale in eight out of 16 patients (3). Other associations are atrial septal defect (2), mitral valve prolapsed (4,5) tricuspid valve prolapse, marfans syndrome, sinus of valsalva aneurysm and aortic dissection (1). Shunt across ASA is more frequently detected with transesophageal echocardiography than with transthoracic echocardiography (1). Association with mitral and tricuspid valve prolapse and other abnormalities, such as Marfan's syndrome and sinus of valsalva aneurysm may point to common inherent connective tissue deficiency (6). Familial clustering of ASA has also been reported (13).

Clinical manifestations

Manifestations attributed to ASA are 1) atrial arrhythmias and 2) arterial embolisms.
Interatrial septal aneurysm can act as an arrhythmic focus, generating focal atrial tachycardias. Hanley et al. (2) noted atrial arrhythmias in 20 out of 80 patients (25%). Mugge A. et al., in a multicentre study of 195 patients, found atrial tachyarrhythmia in 47 patients (24%), and 28 patients (>14%) had atrial fibrillation (1). Schneider B. et al. reported prevalence of atrial tachyarrhythmia in 26% of cases of ASA (8). Mechanism of increased prevalence of atrial tachyarrhythmia in ASA is not clear, though redundancy of atrial septum could be responsible for pathogenesis of arrhythmia.
Arterial embolism is another complication associated with ASA. Presence of ASA tends to aggravate stasis of left arterial (LA) blood flow and predispose to minute LA clots and systemic thrombo embolisms. 
With cardiac embolisms reported in 20-52% of cases of ASA, various studies have found significant association between ASA and arterial embolism (7,9,10). Most patients (70%) had left to right shunts (7), and a higher prevalence of ASA was reported in cerebrovascular accident patients compared with the general population (7.9% vs. 2.2%) (11). A retrospective study by Mugge A. et al. reported that patients with ASA, and especially those with shunts, showed increased frequency of clinical events in their past, compatible with cardiogenic embolism. Atrial septal aneurysm was often the only source of embolism, as judged by transesophageal echocardiography (1). Salmasi A. M. reported higher prevalence of ASA and patent foramen ovale in the Afro-Caribbean population, compared with Indo-Asians, suggesting ASA as a possible cause for increased incidence of stroke in Afro-Caribbeans (12). Mechanism of cardioembolic stroke could be right to left shunting, as detected in most cases of ASA or in the thrombogenic properties of aneurysm itself. A non- ejection click may occasionally be heard, possibly as the IAS aneurysm bulges and tenses within the LA/RA cavity, thus suggesting ASA as one of the causes of systolic click (20).

Diagnosis and treatment

Echocardiography is used to diagnose ASA, either during routine echocardiography or in cases of cardioembolic cerebrovascular stroke and peripheral embolism. Compared with transthoracic echo, transesophageal echo is more sensitive in picking up ASA (1, 7). Cardiac computed tomography and magnetic resonance imaging are also useful for diagnosis of ASA (14, 15).

• Uncomplicated and isolated ASA requires no specific treatment other than follow-up. Patients should be evaluated for presence of thrombus in aneurysms. 
• Therapeutic options for prevention of recurrent strokes in patients with atrial septal aneurysm as well as atrial septal abnormality – including patent foramen ovale (PFO) and ostium secundum atrial septal defect (ASD) - are medical therapy with antiplatelet agents or anticoagulants and surgical or percutaneous closure of the defect.  
• To prevent recurrent paradoxical embolisms in the presence of shunts, it is preferable to close the shunt: transcatheter procedure is now safe and effective and is commonly used for this purpose (16) even though superiority of closure over best medical therapy has not been established (21). 
• In case of atrial arrhythmia, specific treatment is given. In the case of embolic episode, the patient needs antiplatelet drugs, preferably oral anticoagulation for secondary prevention of cardioembolic episode. 
• The efficacy of aspirin therapy is suggested by the French PFO-atrial septal aneurysm (ASA) study. Following 216 patients with cryptogenic stroke and PFO alone showed that recurrent stroke on aspirin was 2.3% after four years, compared with 4.2% in patients with neither a PFO nor an ASA (19).

Conclusion:

The report looks at the chances of finding atrial septal aneurysm in a case of cerebral embolism. Although atrial fibrillation is a well known cause of stroke, presence of atrial septal aneurysm needs some attention as it could be contributory. There is a possibility that atrial septal aneurysm could be a culprit for strokes.